Allergic rhinitis is caused by the response of the autoimmune system in the body to a causative agent in the external environment, and dust, mold, pollen, or the like is known as the causative agent.
A drug therapy, a desensitization therapy, an operative therapy by inferior concha cauterization using a laser, or the like is known as a therapeutic method for allergic rhinitis represented by pollinosis. For the drug therapy, a steroidal anti-inflammatory drug, an immunosuppressive drug, an antihistamine drug, or the like is used; however, this therapy is known to have problems in terms of side effects and efficacy. For example, it is considered problematic in that the steroidal anti-inflammatory drug has side effects such as adrenal atrophy and dysfunction and gastric ulcer (see, for example, Non-patent Document 1), that the immunosuppressive drug has side effects such as infection (see, for example, Non-patent Document 2), and that the antihistamine drug has side effects such as malaise, drowsiness, and dizziness. The antihistamine drug is also known to be unsatisfactory in terms of efficacy compared to the steroidal anti-inflammatory drug and the immunosuppressive drug.
The desensitization therapy is known as a method for suppressing only a concerned antigen-specific immune response by specifying an antigen responsible for allergy and intradermally administering the antigen to induce desensitization; however, it is considered to take several months to several years to exert a sufficient effect. In addition, this therapy is known to have a risk of inducing anaphylactic shock or the like due to the direct systemic administration of an antigen causing allergy, making it necessary to gradually increase its dose from a low dose. In other words, the desensitization therapy is considered problematic in that it not only requires a long-term treatment but also is accompanied by a patient's distress due to injection.
The operative therapy by inferior concha cauterization using a laser is considered problematic in that it not only inflicts a physical distress on patients with allergic rhinitis but also is not a method for radically treating allergic rhinitis.
On the other hand, recently, PDT has been developed that is a method involving administering a compound responsive to light and treating a target area by light irradiation. PDT is simple in treatment, exhibits low invasiveness into a living body, and enables the conservation of an organ, for example; thus, it has recently been a focus of attention as a new method for treating cancer in which consideration is given to quality of life (QOL).
ALA as one of the drugs used for PDT is known as an intermediate in a pathway of pigment biosynthesis broadly present in animals, plants, and fungi, and is typically biosynthesized from succinyl-CoA and glycine by 5-aminolevulinic acid synthetase. Although ALA has no photosensitivity per se, it is known that ALA is metabolically activated to protoporphyrin IX (hereinafter also referred to as “PpIX”) by a series of enzymes of the heme biosynthetic pathway in cells and then specifically directly accumulates in tumor tissue and neovascular vessels, and that, when laser light is irradiated on the site in which PpIX accumulates, cancer cells are degenerate/necrotize by reactive oxygen species generated by the excitation of light, which are represented by singlet oxygen, hydroxyl radical, superoxide, and the like.
Since Professor Kennedy of Queen's University, Canada, reported in 1986 that skin cancer can be treated by applying ALA and irradiating light (see, for example, Non-patent Document 3), methods have been reported for diagnosing and treating lesioned parts of various sites using ALA. For example, tumor diagnosing agents are proposed which have been developed based on the finding that, when ALAs is administered into the body, PpIX derived from the ALAs accumulates in cancer and emits fluorescence by light irradiation (see, for example, Patent Documents 1 and 2).
Because PpIX emits red fluorescence having a peak at a wavelength of 636 nm when receiving excitation light having a wavelength around 410 nm, ALAs are used for the diagnosis of tumor by 5-aminolevulinic acid-based photodynamic diagnosis (ALA-PDD), and is also expected to be used in applications such as the diagnosis of brain tumor or bladder cancer and the prevention of anemia.